Sensor systems for determining at least one parameter of a fluid medium flowing in a line are used, for example, for measuring intake air masses of an internal combustion engine. In particular, such devices may be used in the form of hot-film air-mass flow meters. Other types of devices for determining other, or additional parameters are also conceivable, however, for instance, temperature sensors, speedometers or similar measuring devices, as well as other measuring principles than the hot-film air-mass flow meter principle.
Hot-film air-mass flow meters are discussed in DE 102 53 970 A1, for example. In that text, a device is described which includes a part that is able to be installed, at a predetermined alignment, with respect to a main flow direction, in a line that has the flowing medium flowing through it. A partial flow of the medium, in this context, flows through at least one measuring channel provided in the part, in which a measuring element is situated. Between the inlet and the measuring element, the measuring channel has a curved section for diverting the partial flow of the medium that has entered the measuring channel through the inlet, the curved section going over, during the further course, into a section in which the measuring element is situated. In the measuring channel, in this instance, an arrangement is provided that guides the flow and that counteracts the detachment of the partial medium flow from the channel walls of the measuring channel. Furthermore, the inlet region in the area of the opening, that points counter to the main flow direction, is provided with slantwise or curved areas that are designed in such a way that medium flowing into the inlet area is steered away from the part of the measuring channel that leads to the measuring element. This has the effect that liquid portions or solid parts contained in the medium, based on their inertia, are not able to get to the measuring element and to pollute it.
Devices, such as the one in DE 102 53 970 A1, have to satisfy a plurality of requirements and boundary conditions in practice. These boundary conditions are extensively known from the literature, and discussed, for example, in DE 102 53 970 A1. In addition to the aim of reducing a pressure drop at the devices, altogether by suitable flow technology design, one of the main challenges is further to improve the signal quality of such devices. This signal quality refers particularly to the signal level swing, which is determined, for instance, by the rate of flow of the medium through the measuring channel leading to the sensor element, and refers perhaps to the reduction in signal drift and the improvement in the signal-to-noise ratio. The embodiment of the inlet opening discussed, for example, in DE 102 53 970 A1, by an area repelling fluid particles and dust particles is used particularly for the purpose mentioned—the reduction in the signal drift.
In usual sensor systems of the type described, as a rule, a sensor carrier having a sensor chip mounted on it or in it extends into the measuring channel. The sensor chip may, for instance, be adhered into the sensor carrier or adhered onto it. The sensor carrier may, for example, form one unit with a bottom plate made of metal, onto which an electronic system, a control and evaluation circuit in the form of a circuit board, may also be adhered. The sensor carrier may be designed, for instance, as an extruded-on plastic part of an electronic module. The sensor chip and the control and evaluation circuit may be connected to each other by bonding connections, for example. The electronic module thus created may, for instance, be adhered into the sensor housing, and the entire plug-in sensor may be closed using covers. One example of such a system is discussed in DE 103 45 584 A1 or in EP 0 720 723 B1.
It has been shown, in this context, that the contour of the inflow (leading) edge of the sensor carrier, which extends into the measuring channel, has decisive importance for the signal quality of the sensor system. Thus, it is proposed, for example, in DE 103 45 584 A1, that one should design the inflow edge of the sensor carrier to be rounded off, in order to improve the flow quality at the sensor carrier and at the sensor chip, and to avoid pulsating, nonstationary detachments. In EP 0 720 723 B1 it is analogously proposed that one should design the inflow edge to be rounded off or perhaps to be wedge-shaped, to avoid areas of turbulence (eddies) or areas of detachment on the surface of the sensor chip.
This contouring of the inflow edge of the sensor carrier, using a profile that is rounded off in section, is, however, comparatively costly to implement technically. Thus, the system discussed in DE 103 45 584 A1, for example, requires, as a rule, injection molding the sensor carrier onto the sheet metal component of the bottom plate of the electronic module, which is comparatively costly, from a constructive point of view. It would therefore be desirable to produce the circuit board of the electronic module and the bottom plate as well as the sensor carrier in one piece, and replaced by a single circuit board. In this case, however, a contouring using an inflow edge that is rounded off, as is described in the related art, would be technically only very costly to implement, since using the circuit board limits the choice of the cross section of the sensor carrier, as a rule.